Red hair is a fascinating and relatively rare human trait, and the short answer to whether it is dominant is a definitive no. Red hair is a classic example of a trait governed by recessive inheritance. Affecting only about one to two percent of the global population, this distinctive hair color is a matter of biological pigment production and genetics.
The Chemistry Behind Red Hair Color
Hair color, like skin and eye color, is determined by the presence and ratio of pigments known as melanin. There are two primary types of melanin produced in the body’s pigment cells, called melanocytes: eumelanin and pheomelanin. Eumelanin is the pigment responsible for brown and black colorations, meaning high levels of this substance result in dark hair.
Pheomelanin, in contrast, is characterized by its reddish-yellow hue. Red hair occurs when the melanocytes produce a high concentration of pheomelanin and very little eumelanin. The specific shade of red—ranging from bright copper to deep auburn or strawberry blond—is determined by the exact combination and total amount of these two melanins.
The Role of the MC1R Gene
The switch that controls the production of these two melanin types is directed by the melanocortin 1 receptor, or MC1R, gene. This gene provides the instructions for creating a receptor protein that sits on the surface of the melanocyte cells. When the MC1R receptor is activated, it signals the cell to synthesize the dark pigment, eumelanin.
The version of the gene that leads to red hair contains variants that are often described as “loss-of-function” mutations. These variants prevent the MC1R receptor from functioning properly, meaning it cannot receive the signal to produce eumelanin. As a result, the pigment pathway defaults to producing the red-yellow pheomelanin instead.
Understanding Recessive Inheritance
The reason red hair is considered a recessive trait lies in how genetic information is passed down and expressed. Every person inherits two copies of the MC1R gene, one from each biological parent. The version of the gene that functions normally and produces dark hair is the dominant allele, while the variant that leads to non-functional receptors and red hair is the recessive allele.
For red hair to physically manifest, an individual must inherit two copies of the recessive MC1R variant, one from each parent. If a person inherits one dominant, functional copy and one recessive, non-functional copy, they will typically have non-red hair, such as brown or blonde.
Individuals who possess one recessive variant but do not have red hair are called carriers, and they can pass the recessive gene to their children. This mechanism explains why non-redhead parents who are both carriers can still have a child with red hair, as there is a 25% chance of the child inheriting both recessive copies.
Associated Traits and Genetic Links
The variants of the MC1R gene responsible for red hair are also linked to several other physical and physiological characteristics. The shift toward pheomelanin production is also responsible for the pale skin tone and frequent presence of freckles seen in redheads. Because pheomelanin does not offer the same UV protection as eumelanin, individuals with red hair are naturally more susceptible to sunburn and have an increased risk of developing skin cancer.
Beyond pigmentation, the MC1R gene variants have also been associated with altered pain perception. Research suggests that people with the red hair gene may require higher doses of certain anesthetics, such as local dental anesthetics, to achieve the same level of pain relief. The MC1R receptor is found not only in pigment cells but also in the brain, where it is part of the pathway that processes pain.
This genetic linkage explains why the red hair trait frequently appears alongside fair skin and light-colored eyes, creating a characteristic suite of features common in populations of Northern and Western European ancestry. The concentration of red hair is highest in countries like Ireland and Scotland, which have the highest percentage of redheads per capita globally.